/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        if(head==null){
            return head;
        }
        ListNode p1 = head;
        ListNode p2 = head.next;
        while(p2 != null) {
            if(p1.val == p2.val) {
                p1.next=p2.next;
                p2=p1.next;
            }else{
                p1=p2;
                p2=p2.next;
            }
        }
        return head;
    }
}